Tomatoes growing side-by-side in red and black plastic mulch.Q: I’m thinking of trying that plastic red mulch you once wrote about for under my tomatoes this year. Does it come in sheets or shredded? If it’s in sheets, how do you water properly?

A: Red mulch is one type of colored plastic sheeting. Researchers have found that reflected light from different colors of plastic mulch can affect yield, soil temperatures and even bugs on crops.

Penn State research found that pepper yield increases with silver mulch underneath, for example, while yellow mulch attracts cucumber beetles (a trait useful for growing a “trap crop” to reduce pesticides). Penn State’s studies found that red mulch increases tomato yield by up to 12 percent and might slightly delay the incidence of early blight.

Like most things scientific, a whole lot of variables revolve around what kind of response you might see in your garden, including the brand of plastic sheeting used, weather and probably even the variety of tomatoes you use.

I took a look at what ordinary gardeners who’ve used red plastic are saying online, and while some noticed a difference, even more say they didn’t notice much, if any, difference. I’ve used it and didn’t notice any difference from either the black plastic or straw mulch that I usually use.

Black plastic is usually cheaper and offers the benefits of any dark mulch over bare ground -- retains soil moisture, stops weeds, keeps the sun from overheating the soil and discourages soil-borne disease spores from splashing up on your new plants.

Part of the fun of gardening is doing your own experiments, though. So get a few different kinds and colors of mulch and do your own trials.

For any plastic mulch, keeping the soil underneath damp enough can be an issue -- especially in raised beds. Some rain will get in the openings around your plants, but in general, your best results will be installing drip lines underneath the plastic to make sure your plant roots get regular moisture.